Can You Hear Me 

Bass Knob

Bass knob types 

In line on the phono sub out 

This is an option if you have an amp that does not have a sub control on board this is designed to be in the line to the amp where it would allow control of the sub woofer

Amp specific using a RJ9 connection (others may come with the one above)

This type is am specific due to type of connection (Rj9) unless the connection pin layout is the same as the one needed for your specific use there are a few with an additional if it does this will be in manual  the as to when an  amp control which is like an extra boost when knob is turned to full

Sub Woofer

Woofers and sub woofers are large speakers designed to reproduce only low-frequency bass sounds.Good low bass is a necessity for a great audio system. Smaller speakers can't reproduce realistic low-frequency sounds, so for this a good system really needs a separate sub-woofer. Some systems take it one step further and use a specialized mid-bass driver to handle the troublesome frequencies between low bass and mid-range. Tweeters are the smallest of the specialized drivers and reproduce the upper treble frequencies.

DSP

You may ask "What does DSP stand for ?"  well Digital Signal Processor these units adjust sound in real time and have the ability to improve on a sound stage with fine adjustment of the frequency range for a cleaner audio playback you will have your low to mid range versions of the units like this then you also get high end with a lot more scope for adjustment of the sound stage

Sub Box

The sub enclosure depending on where you stand on this as you have two options you can have a ported enclosure or none ported enclosure dependent upon your needs and the sound stage you are aiming for this will play a part in whether it is or is not ported as we well know with sound comes vibration an with that comes air displacement as the sub-woofer face moves back an forth creating the sound none ported boxes tend to be larger due to needing additional space to accommodate the minimum cubic feet of the sub-woofer which is a guide line for a sub-woofer to function at its optimum proficiency which also limits the size and power rating of a sub the can be used as in car audio space is a premium.    

Ohm’s law may be expressed mathematically as V/I = R 

V (in units of volts)  /  I current (amperes) = R (The resistance)

Speaker Cable

Speaker cables are an important cog in your sound stage as good cable will transmit your clean audio to your speaker. When using high end speaker you want a high end cable to reduce degradation of sound in transit  an to ensure minimal effect on the speakers current ohm's rating the less the better

Speaker plates/connection

there are a few different types available some in picture above there are a few other styles an alternatives to connecting your sub woofer enclosure but there are some who don't like to use a speaker plate at all and instead drill a hole just big enough for the wire, to minimize the weakening of the sub woofer enclosure dependent on size of the plate

Mono Block Amp

The Amplifier
A car stereo system has to have an amplifier to increase the power of an audio signal so it's strong enough to move the speakers and create sound. Amplification is a two-stage process handled by a pre-amp and a power amplifier.

The pre-amp is usually housed inside the head unit and takes data from a radio, CD player or other audio source and prepares it for the power amplifier. This process includes slightly boosting the audio signal, which makes it compatible with the input of the power amplifier and ensures that it's resistant to noise that can radiate from other electronics in a vehicle. The power amplifier then takes the pre-amp low-level signal and significantly boosts it so it can move the speakers and create sound.

Many head units have a small, built-in low-power amplifier that can "drive" smaller speakers. This allows the audio system to be reduced to just a head unit and a few speakers. But better sound requires more power. So higher-end systems have separate power amplifiers that are mounted away from the head unit due to their size and the heat they generate.